Mechanical And Electrical Reliability of a Chronically Implanted Metal-Polyimide Electrode Array
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1116-I09-12
Mechanical And Electrical Reliability of a Chronically Implanted Metal-Polyimide Electrode Array John D. Yeager1, Derrick J. Phillips2, David M. Rector2 and David F. Bahr1 1
Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164, USA 2 Veterinary and Comparative Anatomy, Pharmacology & Physiology, Washington State University, Pullman, WA 99164, USA ABSTRACT A flexible electrode array consisting of a thin metal film on a polymer substrate has been developed for neural implantation in rats. The biocompatible arrays record cortical brain signals from awake and mobile rats in order to gather significant neurological data. Four point bend testing of the metal-Kapton system has been used to characterize the interfacial toughness, and therefore the mechanical durability, of the array. Several different adhesion layers on were evaluated using this method. Use of a titanium-tungsten interlayer increases the mixed-mode fracture toughness from approximately 1 J/m2 to approximately 2 J/m2, while a titanium interlayer provides a toughness of more than 4 J/m2. Gold-Kapton arrays were implanted in rats for periods exceeding 200 days, and neural recordings were taken frequently. The arrays exhibit excellent long-term reliability, with no decrease in signal recording capability over the course of the implantation. INTRODUCTION The recording of brain signals in rats has great importance to the neuroscience and veterinary fields. The primary signals of interest for this study are population action and excitatory post synaptic potentials, which are generated by auditory stimulation. The objective of this research is thus to record these neural signals from the cortex with high spatial precision and minimal damage to the rat. Investigation of the intensity, response time and duration of the signals may give valuable insight into the interpretation of external stimuli by the brain [1]. Some researchers have found that direct implantation of a grid of microwires in mammals allows for recording signals from individual neurons [2]. The principal drawback of the microwire technique for measuring neural signals is that it requires penetration of brain tissue and removal of large areas of the skull. This mechanical trauma can lead to long term inflammation and formation of scar tissue, resulting in decreased signal measurement [3]. In addition, the surgical procedure for such an electrode array involves the removal of large areas of the skull [1]. The rat is necessarily induced into a coma during recording, resulting in limited signal measurement as well as requiring termination afterwards. In contrast, thin and flexible electrodes have successfully been used to penetrate through small slits in the skull and record cortical signals, removing the need to penetrate tissue as well as reducing overall trauma [4,5]. Auditory stimulation induces population action and excitatory post synaptic potentials which can be recorded directly from the cortical surface, and therefore it is not necessary to penetrate
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